[media]: refactoring AudioSystem.cpp to C++ style, part 2 am: 8e1146c0

Original change: https://android-review.googlesource.com/c/platform/frameworks/base/+/2624409



Change-Id: I15f3e6f85769dc8368817f7ed150b7d0394bd714
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>